1. Field of the Invention
The present invention relates to a capacitance type displacement detection apparatus and in particular to crosstalk suppression between a transmission electrode and a detection electrode.
Further, the present invention relates to a capacitance type displacement detection apparatus and in particular to crosstalk suppression between a signal line group for supplying signals to a transmission electrode and a signal line group for transferring signals from a detection electrode.
2. Description of the Related Art
A capacitance type displacement detection apparatus, which will be hereinafter referred to as capacitance type sensor, comprises a transmission electrode, a reception electrode and a detection electrode. The transmission electrode and the reception electrode are formed on two scales placed in a relatively movable manner. The detection electrode detects change in the magnitude of capacity coupling between the transmission electrode and the reception electrode with a movement of the scale.
Specifically, as the transmission electrode, a plurality of electrodes are arranged so as to form a transmission electrode group. At least three types, preferably eight or more types of AC signals different in phase by predetermined phase angle are supplied to the electrode group from a processing circuit (circuit board) using a signal line group. When the opposed scale is displaced, a composite signal responsive to the displacement occurs on the reception electrode. The composite signal is detected with the detection electrode and is transferred to the processing circuit using the signal line group. The detection electrode comprises at least one electrode, preferably two or more electrodes. If the number of electrodes is two or more, a signal is detected with the two electrodes having differential relationship. By using the difference therebetween, noise contained in the detected signal can be removed and therefore the detection accuracy is increased.
However, if the transmission and detection electrodes are formed nearby on the same scale with the demand for miniaturizing the sensor, the signal lines for supplying a plurality of signals (eight types of signals) to the transmission electrode group and the detection electrode are directly capacity-coupled, causing crosstalk to occur; this is a problem. Particularly, if the distances between the detection electrode and the eight signal lines vary, the degree of the crosstalk of one of the signal lines affecting the detection electrode differs from the that of another. Thus, if the differential relationship is used, the crosstalk component remains and it becomes difficult to detect displacement with high accuracy.
Of course, as shown in FIG. 13, a configuration wherein a transmission electrode 210 and detection electrodes 212 formed on the same scale are placed away from each other as much as possible and electromagnetic shielding is provided between the two electrodes is also proposed. In this configuration, however, the electrode section area is increased and thus it becomes disadvantageous for miniaturizing the sensor.
In addition, it is also proposed to form integrally a signal line group for supplying signals to a transmission electrode group and a signal line group for transferring signals from a detection electrode group on an FPC (flexible printed circuit); however, if both the signal line groups are formed nearby, crosstalk of mixing signals in the transmission signal line group into the detection signal line group occurs; this is a problem. Particularly, if distances between the transmission signal line group and the detection signal line group vary, the degrees of crosstalk differs. Thus, if the differential relationship is used, the crosstalk component remains and it becomes difficult to detect displacement with high accuracy; this is also a problem.
Of course, as shown in FIG. 14, a configuration wherein a transmission signal line group 310 and a detection signal line group 312 formed on the same FPC are placed away from each other as much as possible, and electromagnetic shielding is provided between the two signal line groups is also proposed. In this configuration, however, the FPC area is increased and thus it becomes disadvantageous for furthermore miniaturizing the sensor.
It is therefore a first object of the invention to provide an apparatus capable of suppressing degradation of detection accuracy caused by crosstalk between a transmission electrode (containing signal lines) and a detection electrode without incurring an increase in the area of an electrode section.
It is a second object of the invention to provide an apparatus capable of suppressing degradation of detection accuracy caused by crosstalk between a transmission signal line group for supplying signals to a transmission electrode group and a detection signal line group for transferring signals from a detection electrode group without incurring an area increase.
The first object according to the present invention can be achieved by a capacitance type displacement detection apparatus having a transmission electrode and a detection electrode formed on one scale and capacity-coupled with a reception electrode formed on the other scale opposite to the one scale. The apparatus comprises: a plurality of transmission signal lines disposed on the one scale at substantially equal distance from the detection electrode for supplying signals to the transmission electrode.
To make the distances between the plurality of signal lines and the detection electrode substantially equal, the distances between the respective signal lines and the detection electrode are made substantially equal, and in addition, if a plurality of the detection electrodes exist, the distances between the signal lines and one detection electrode and the distances between the signal lines and another detection electrode are made substantially equal. The amount of crosstalk given by each signal line to the detection electrode depends on the distance from the signal line. Then, the distances between the respective signal lines and the detection electrode are made substantially equal, namely, are made uniform, whereby variations in the crosstalk amounts from the signal lines can be suppressed. If a plurality of the detection electrodes exist, the distances between the signal lines and one detection electrode and the distances between the signal lines and another detection electrode are made substantially equal, namely, are made uniform. Accordingly, the crosstalk amounts given to the detection electrodes can be made equal for suppressing variations in the crosstalk amounts between the detection electrodes.
Here, xe2x80x9csubstantially equal (or same) distancexe2x80x9d means equal distance to such an extent that the ratios of the crosstalk components mixed from the transmission signal lines can be regarded substantially equal on the detection electrode.
Preferably, the plurality of signal lines have a multi-layer structure. To make the distances between the respective signal lines and the detection electrode substantially equal, preferably the signal lines are made to cross each other and the distances are made substantially equal as a whole. However, if the signal lines are formed in the same layer, they come in contact with each other and it is made impossible to supply a plurality of signals to the transmission electrode. The signal lines are placed in a multi-layer structure, whereby it is made possible to cross the signal lines without bringing them into contact with each other, and the distances between the respective signal lines and the detection electrode can be made substantially equal easily.
Further, the first object according to the present invention can be achieved by a capacitance type displacement detection apparatus having a transmission electrode and a detection electrode formed on one scale and capacity-coupled with a reception electrode formed on the other scale opposite to the one scale. The apparatus comprises: a plurality of transmission signal lines disposed on the one scale for supplying signals to the transmission electrode, the transmission signal lines having a differential relationship and disposed adjacently to each other with respect to the detection electrode. The signal lines having the differential relationship are made adjacent to each other, more specially, the signal lines having the differential relationship are disposed at substantially equal distance with respect to the detection electrode. Accordingly, the crosstalk amounts given by the signal lines to the detection electrodes can be set almost equal and can cancel each other out. The xe2x80x9cdifferential relationshipxe2x80x9d means the mutually opposite phase (180-degree phase shift) relationship.
The second object according to the present invention can be achieved by a capacitance type displacement detection apparatus having a transmission electrode group and a detection electrode group formed on one scale and capacity-coupled with a reception electrode formed on the other scale opposite to the one scale. The apparatus comprises: a transmission signal line group for supplying signals to the transmission electrode group, the transmission signal line group having at least two transmission signal lines and disposed on a first wiring layer; and a detection signal line group for transferring signals from the detection electrode group, the detection signal line group having at least two detection signal lines and disposed on a second wiring layer different from the first wiring layer, the detection signal lines having a differential relationship and disposed at substantially equal distance from the transmission signal line group. The transmission signal line group and the detection signal line group are not placed on the same plane of an FPC, for example, unlike those in the related art and are formed in different layers of a multi-layer structure, so that the transmission signal line group and the detection signal line group can be placed away from each other while area increase is suppressed. The signal lines having differential relationship, contained in the detection signal line group, namely, the signal lines for transferring signals different in phase by 180 degrees are placed at substantially equal distance from the transmission signal line group, whereby the crosstalk components mixed into the signal lines having differential relationship become substantially equal and difference calculation is executed, whereby the crosstalk components can be removed. Here, the term xe2x80x9cgroupxe2x80x9d of xe2x80x9ctransmission signal line groupxe2x80x9d and xe2x80x9cdetection signal line groupxe2x80x9d means a plurality of signal lines. In addition, the term xe2x80x9csubstantially equal distancexe2x80x9d means equal distance to such an extent that the ratios of the crosstalk components mixed from the signal lines contained in the transmission signal line group can be regarded substantially equal on two detection signal lines.
In the invention, preferably an electromagnetic shielding layer is formed between the layer where the transmission signal line group is formed and the layer where the detection signal line group is formed. The electromagnetic shielding layer is provided, whereby the crosstalk component itself can be attenuated.
In the invention, forming the detection signal line group in a plurality of layers is also preferred. The detection signal line group is separated into a plurality of layers, whereby mixing of the crosstalk components from the transmission signal line group can be controlled and suppressed more reliably.
The second object according to the present invention can be also achieved a capacitance type displacement detection apparatus having a transmission electrode group and a detection electrode formed on one scale and capacity-coupled with a reception electrode formed on the other scale opposite to the one scale. The apparatus comprises: a transmission signal line group for supplying signals to the transmission electrode group, the transmission signal line group including at least two transmission signal lines having a differential relationship and disposed on a first wiring layer; and a detection signal line for transferring a signal from the detection electrode, the detection signal line disposed on a second wiring layer different from the first wiring layer at substantially equal distance from the transmission signal lines having the differential relationship. If one detection electrode rather than a plurality of detection electrodes exist, the transmission signal line group and the detection signal line are formed in different layers, whereby they can be placed away from each other. If one detection signal line only exists, the difference cannot be calculated, but the distances between the signal lines having differential relationship, contained in the transmission signal line group and the detection signal line are made substantially equal, so that the crosstalk from one signal line and that from another cancel each other out and noise can be decreased. Forming an electromagnetic shielding layer between the layer where the transmission signal line group is formed and the layer where the detection signal line is formed is also preferred.